The use of rock phosphates, combined with proper management of soil microorganisms able to solubilize phosphate, is an alternative for reducing the costs of P fertilization. However, both practices require prior assessment of the potential of the rhizospheric microbiota in solubilizing P sources with low reactivity under field conditions. The objective of this study was to evaluate the potential of soil microbes to solubilize Ca, Fe, and Al phosphates, as well as Araxá and Catalão rock phosphates, in rhizospheric and bulk soil samples from hybrid Eucalyptus grandis × E. urophylla plantations located at three points in a typical toposequence from the state of Minas Gerais. Additionally, we evaluated the activity of acid and alkaline phosphatases under the same experimental conditions. The rhizospheric microbiota of plants from the top of the slope and from the lowland showed higher solubilization potential of Ca phosphate (5,745.09 and 6,452.80 μg P, respectively), whereas the soil from along the slope showed no difference among the inorganic sources tested. Catalão rock phosphate was the natural phosphate source with highest solubilization potential (1,209.71 μg P) by soil microbiota under the conditions evaluated. The final pH of the culture medium was negatively correlated with the values of solubilized P, indicating that acidification of the environment is one of the mechanisms used by soil microbiota in phosphate solubilization in vitro. The activity of acid and alkaline phosphatases was higher in the rhizosphere of plants from the top of the slope, an area with higher organic matter content. No clear correlation between phosphate solubilization potential or phosphatase activity with the average diameter at breast height of trees was observed. This study demonstrates the effect of topography on the solubilization potential of soil microbes, which is positively influenced by the organic matter content of the soil.
microbial activity; phosphomonoesterase; rock phosphate; soil microbiota; rhizosphere